This invention relates to a process for the generation of mechanical energy in the ammonia oxidation step of a process for the production of nitric acid, i.e. the step wherein ammonia is burned to form NO.sub.x.
Processes for nitric acid production are known in which ammonia is oxidized to form NO.sub.x gases; the oxidation normally takes place at a temperature of 800.degree. to 970.degree. C. The downstream absorption of NO.sub.x gases in water to form HNO.sub.3 is carried out at substantially lower temperatures in order to meet the reaction requirements. Therefore, the NO.sub.x gas stream must be cooled prior to entering the absorption unit.
According to the known processes, a multi-step cooling method is used. In the first step the NO.sub.x gases are cooled at a high temperature in order to utilize the process heat. Hence, a steam generator is connected directly to the burner and used for the generation of steam. Furthermore, the process heat in the NO.sub.x gases may also be use for tail gas heating, etc.
After cooling the NO.sub.x gases to approximately 200.degree. C., however, the gases are further cooled with water without making use of their residual heat. Consequently, the known cooling processes employed in this case require large quantities of cooling eater causing higher operating costs, or larger heat exchangers must be installed which results in higher investment costs.